The disclosures herein relate in general to digital signal processing, and in particular to a method and system for excursion protection of a speaker.
Many portable electronic devices are relatively small and inexpensive. Accordingly: (a) such devices may have speakers that are relatively small and inexpensive; and (b) drive units of the speakers may have relatively low power handling capacity and relatively low sensitivity, which increases risk that a powerful amplifier might push them to power handling and mechanical limits in an attempt to reach higher sound volumes. Causes of speaker failure include: (a) over-excursion (e.g., excessive backward and/or forward movement) of the speaker's diaphragm; and (b) overheating of the speaker's voice coil. For example, if the speaker receives an input voltage signal whose level is relatively high and whose frequency is relatively low, then the speaker's voice coil may exit its safe gap and thereby damage the speaker. In some cases, a sensor can directly monitor excursion of the speaker's diaphragm, but the sensor's size and expense may be impractical for many portable electronic devices.
In a conventional dynamic range compression (“DRC”) technique, the input voltage signal is received by a dynamic range compressor. In one example: (a) if the input voltage signal's amplitude exceeds a threshold's limit, then the signal is dynamically compressed by the dynamic range compressor; and (b) otherwise, the signal is unmodified by the dynamic range compressor. However, the input voltage signal's amplitude is nonlinearly related to excursion of the speaker's diaphragm, so that: (a) DRC may unnecessarily compress the signal (in a manner that distorts sound and/or reduces perceived loudness of the speaker), despite peak excursion of the speaker already being within a safe operating range; and/or (b) over-excursion of the speaker may still occur, despite the input voltage signal's amplitude being within the threshold's limit. Accordingly, a different technique would be useful for keeping such excursion within a safe operating range, in order to protect the speaker.